Updated September 4, 2025:
Progress Report 1
Objectives:
1. Conduct a literature review to identify pollinators found within corn and soybean fields to support field observations
2. Determine diversity and visitation of pollinators in traditional corn and soybean rotations compared to alternative corn-soybean crop rotations
Progress:
Objective 1. We have completed a search and hired a PhD student to help lead the literature review and carry out field research for Summer 2025. Additionally, we conducted preliminary searches in Web of Science and EBSCOhost to find peer-reviewed literature on pollinators visiting soybean and corn fields. Restricting articles to the USA, we are reviewing nearly 300 articles per crop per database (see attachment Table 2).
We are extracting pollinator species data from historical field data from peer-reviewed publications. Currently, we have found Halictids (sweat bees) are the most abundantly found species in soybeans and corn fields in the Midwest (e.g., Gill and O’Neal 2015, St. Clair et al. 2022). The family of insects that include bumble bees and honey bees (Apidea) are the second most commonly found species. From these data, we currently found two species being considered for listing under the ESA in soybean fields. The American bumble bee (Bombus pensylvanicus) and the monarch butterfly (Danaus plexippus). The American bumble bee is petitioned for listing and has been found in soybean fields of Indiana and Nebraska, but not Iowa (St. Clair et al. In Preparation). The monarch butterfly is proposed for listing as threatened and has also been observed in soybean fields across the Midwest, including Iowa. However, we do not know how these two species use crop fields. They may be using soybean flowers for nectar or flying within fields to find other flowering plants. Monarchs are unlikely to use soybeans for nectar, but other bumble bee species have been observed foraging in soybeans (Levenson et al. 2022).
The next step will be reviewing articles to remove duplicates and irrelevant articles. Then, we will start extracting data from all papers and developing our review article. We will collect information on species richness, distance from field edge, location, surrounding land use, presence of conservation practices, and any toxicology information.
We are also leveraging Iowa Soybean Association (ISA) funds by partnering with a recently hired entomologist (Michael Killewald), who has trained with Dr. Jason Gibbs, associate professor of Entomology and curator of the R. E. Roughley Museum of Entomology at the University of Manitoba. Michael’s salary does not come from ISA, but his research interests overlap with those of this project. He has agreed to work with us to add more data to our review. Michael is working with our team to determine if bumble bees in the Iowa State University collection include the American bumble bee and if these preserved specimens contain pollen from soybeans. Michael will help train the graduate student in the area of pollen and bee identification and compile these data sets to help us determine if bumble bees are feeding on soybean and corn pollen.
Objective 2. We conducted preliminary pollinator surveys (not paid for by ISA) in summer 2024 to determine when alternative crop species flower and what pollinators are present. We originally planned to survey pea, sunflower, buckwheat, balansa clover, red clover, and sunn hemp with 1) active surveys where an observer walked through fields for 5 minutes, recording all pollinator species observed on flowers and 2) passive surveys where a video camera was placed by a flowerhead for 4 hours to observe all visiting pollinators. Based on these data we will survey pea, sunflower, buckwheat, and red clover in 2025 since they flowered during the corn and soybean growing season. The majority of pollinators were honey bees (see attachment Table 2), but we did observe monarchs using sunflowers for nectar (see attachment Figure 1).
For the next steps, we will be meeting as a group to finalize plans for Summer 2025 pollinator surveys. The PhD student will be visiting representative fields across Iowa to survey pollinators.
Benefits to Soybean Farmers Soybean farmers will provide this necessary information to help the EPA make science-based changes to their Insecticide Strategy.
Literature Cited:
Clair, A.L.S., Zhang, G., Dolezal, A.G., O’Neal, M.E. and Toth, A.L., 2022. Agroecosystem landscape diversity shapes wild bee communities independent of managed honey bee presence. Agriculture, Ecosystems & Environment, 327, p.107826.
Gill, K.A. and O’Neal, M.E., 2015. Survey of soybean insect pollinators: community identification and sampling method analysis. Environmental entomology, 44(3), pp.488-498.
Levenson, H.K., Sharp, A.E. and Tarpy, D.R., 2022. Evaluating the impact of increased pollinator habitat on bee visitation and yield metrics in soybean crops. Agriculture, Ecosystems & Environment, 331, p.107901.
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